There are known printers by various systems such as an ink jet system, thermal recording system, and wire dot recording system. On the other hand, with the spread of a digital camera or personal computer, there has been a demand for a printer in which digital image data can be recorded with high precision. It is to be noted that a printer for printing not only images but also characters. The images to be printed include the characters.
However, the printer has a problem that with a high minuteness of image quality, the number of pixels increases, and a print speed is reduced. To solve the problem and increase the print speed, the following methods have heretofore been proposed.
In a first prior method, a head having a large number of recording pixels is provided in order to increase an area be recorded or printed by one scanning operation. For example, in a recording head of the ink jet system, a multi-nozzles head having a large number of nozzles for jetting ink droplets is used.
FIG. 8 is a schematic view of such conventional method. In FIG. 8A, reference numeral 10 denotes a recording sheet (print sheet, recording material) which is conveyed in a sub scanning direction shown by an arrow 12, that is, in an upward direction on the drawing. 14 is a recording head of a color ink jet system, which is conveyed in a main scanning direction shown by an arrow 16, that is, reciprocated in a left to right direction on the drawing. For the recording head 14, as shown in an enlarged view of FIG. 8B, nozzles for jetting ink droplets having different colors, i.e., yellow (Y), magenta (M), cyan (C) and black (BK), are aligned as one set in the main scanning direction, and a large number of the same sets are arranged in the sub scanning direction.
In a second conventional printing method, a plurality of small-sized heads are combined or integrated to provide capabilities substantially similar to those of the multi-nozzle head. FIG. 9 is a schematic view showing this method. In this method, four small heads 18A to 18D having positions deviated with each other are combined with minute precision to form a multi-nozzle head 20. Here, the small heads 18A to 18D are combined in such a manner that recording areas are divided in the main scanning direction 16 and continuously arranged in the sub scanning direction 12.
As shown in a schematic view of FIG. 10, a third prior proposed method uses a plurality of independent printers 22A to 22D contained in a common case 24. The same image data of the same page or different image data of different pages are allocated to the respective printers 22A to 22D, the image data are recorded simultaneously in parallel with one another, and printed sheets are collected in one discharge tray 26.
In the first prior method as shown in FIGS. 8A, 8B, the recording head 14 is large in size. That is, a dimension 28 of the recording head 14 in the sub scanning direction increases as seen in FIG. 8A. However, when the head 14 is enlarged, the number of nozzles also increases. Therefore, problems occur that it becomes difficult to manufacture the head, dispersions generated in performance characteristics of the respective nozzles increase, and manufacturing yields of the heads are deteriorated.
Moreover, since a recording surface (ink jet surface) of the head 14 is disposed opposite to a platen (not shown) via the recording sheet 10, feed rollers for feeding the recording sheet 10 are positioned on the upstream and downstream sides of the platen. Therefore, an interval between the feed rollers is broadened, and the recording sheet 10 easily floats up above the platen. As a result, the distance between the recording sheet 10 and the ink nozzles of the head 14 fluctuates and this sometimes causes the deterioration of a recorded image quality.
In the second prior proposed method as shown in FIG. 9, it is difficult to combine the small heads 18A to 18D with good precision, high precision is not easily achieved, further the whole dimension of the multi-nozzle head 20 increases, and therefore the heads are enlarged. Moreover, the head 20 becomes heavy, and a width of the head 20 in the main scanning direction is broadened. This causes problems that a movement distance of the head 20 increases during main scanning and as a result a recording speed drops.
Moreover, since the dimension of the multi-nozzle head 20 in the sub scanning direction also increases, the interval between the feed rollers on the upstream and downstream sides of the multi-nozzle head 20 should be broadened. Therefore, similarly as the first conventional method, the distance between the recording sheet 10 and head 20 fluctuates and this causes a problem of the image quality deterioration.
In the third method as shown in FIG. 10, since a plurality of printers are substantially used, apparatus enlargement and cost increase are caused.